Secret Trove May Resolve 'Copenhagen'

By JAMES GLANZ

Published: October 20, 2001

After more than half a century, historians and scientists still cannot agree on why the Nazis were never able to develop an atomic bomb, or on why the leader of their bomb program, the physicist Werner Heisenberg, visited his old mentor Niels Bohr in occupied Denmark in 1941.

The uncertainty about that meeting is at the center of the award- winning Broadway play "Copenhagen," by the British playwright Michael Frayn. Now, partly as a result of the attention generated by the play's success last year, the Bohr family plans to release previously unpublished, and largely undisclosed, documents by Bohr about the meeting, including a strongly worded letter he wrote to Heisenberg about it but never sent.

Historians who have seen the letter hint that it suggests that Heisenberg was not quite the hero the play made him out to be. But they refuse to provide further details until the formal release, expected before the end of this year.

The uncertainty of the play, and the historical record, revolves around competing explanations for why Heisenberg went to Copenhagen for the meeting. Was he trying to pump Bohr for information about the Allied bomb program? Or did Heisenberg want to assure Bohr that he would stop the Nazi bomb program if Allied scientists agreed not to build one either?

Whatever Heisenberg said, Bohr was so shaken by the meeting that he never spoke publicly about it after the war. The answer to that question could shed light on why Heisenberg, one of history's greatest physicists, winner of the 1932 Nobel prize in physics and author of Heisenberg's uncertainty principle, never succeeded in building atomic weapons for Hitler.

"Copenhagen" leaves those questions unresolved by what Heisenberg calls, in the last line of the play, "that final core of uncertainty at the heart of things." Also left open is whether Heisenberg sabotaged the bomb program, as some historians have maintained, or tried his best for Germany and simply did not succeed.

But at a conference on the play last month in Copenhagen, the Bohr family unexpectedly announced that it would release 11 unpublished documents written by Bohr about the meeting. Those documents include what is said to be an angry letter that Bohr, who fled Denmark in 1943 and joined the Manhattan Project in the United States, wrote to Heisenberg after the war but never sent.

"The Bohr family has come to regard speculation about the content of this material as more harmful than its actual release," said Dr. Finn Aaserud, director of the Niels Bohr Archive in Copenhagen, who is a spokesman for the family. He said the release would probably take place by year's end.

The existence of that letter became generally known only last year at a conference on the play held at the Graduate Center of the City University of New York. There, Dr. Gerald Holton, an emeritus professor of physics and of history of science at Harvard, revealed that the Bohr family asked him and two others, now dead, to look at the letter in the 1980's and make recommendations on how to deal with it.

"We were all three of us astounded by the letter," Dr. Holton said in an interview, adding that the others were Abraham Pais, a physicist and historian, and McGeorge Bundy, an adviser to Presidents John F. Kennedy and Lyndon B. Johnson.

Dr. Holton, who urged the family to preserve the document for history, said he would not reveal its precise contents before the impending release. But he speculated that the usually soft-spoken Bohr had decided not to send the letter because of its stiff language.

The letter contains "the missing part of the whole story," Dr. Holton said elliptically. The documents may be the last way to learn more about the meeting, since Bohr died in 1962 and Heisenberg in 1976.

Mr. Frayn has said his play was inspired by "Heisenberg's War: The Secret History of the German Bomb," a 1993 book by the journalist Thomas Powers, who maintained that Heisenberg threw the bomb program off course so that Hitler would not have atomic weapons.

In an interview, Mr. Powers said he believed Heisenberg traveled to Copenhagen to offer a quid pro quo: German scientists would not build a bomb if Allied scientists did not, either. "It was a crazy idea but a brilliant idea," Mr. Powers said.

Others are angered by the play and by Mr. Powers's book, saying that Heisenberg's attempt to play down his efforts for Hitler after the war may have been what upset Bohr.

"If you sup with the devil, you'd better have a long spoon," said Dr. Jeremy Bernstein, a theoretical physicist and author of "Hitler's Uranium Club," a 2001 book on secret recordings of Heisenberg and other members of the bomb program. "Those people collaborated with a vile regime."

Mr. Frayn said in an interview that he was well aware that some historians already believed there was no uncertainty at all about why Heisenberg went to Copenhagen.

"The only thing that reassures me slightly is when they then go on to say exactly the explanation they're certain of," Mr. Frayn said, "and it turns out to be mostly different from the explanation that somebody else is certain of."